Arc interrupting molding composition and electrical apparatus made therefrom



March 22, 1966 P. w. .JONES ETAL 3,242,257

ARC INTERRUPTING MOLDING COMPOSITION AND ELECTRICAL Filed Sept. 17, 1965 APPARATUS MADE THEREFROM 2 Sheets-Sheet l INVENTORS. P41/z nf. fan/5J' BY wafer t Way/wm March 22, 1966 P. w, JONES ETAL 3,242,257

ARC INTERRUPTING MOLDING COMPOSITION AND ELECTRICAL APPARATUS MADE THEREFROM Filed Sept. 17, 1963 2 Sheets-Sheet 2 I NVENTORS PAM 144 /m/ff BY @55W i Mad/wmf United States Patent ARC INTERRUPTING MOLDING COMPQSITION AND ELECTRICAL APPARATUS MADE THERE- FROM Paul W. Jones and Robert E. Wilkinson, Lafayette, Ind., assignors to Rostone Corporation, Lafayette, Ind., a corporation of Indiana Filed Sept. 17, 1963, Ser. No. 309,496 27 Claims. (Cl. 174-137) This invention relates to electrical apparatus, and to improvement of the arc-interrupting and track-resistant characteristcs of electrical insulating elements and of apparatus embodying such elements. The invention relates to the compositions of such elements and especially to molding compositions containing substantial proportions of hydrated alumina, and involves the addition to the molding compositions of addition elements which increase the arc-interrupting capacity of electrical moldings and apparatus made therefrom. l

By arc-interruption, we mean to include arc-suppression and arc-quenching, and to cover interruption of various arcing phenomena, whether in the form of active arcs such as occur between separating switch contacts or as overload arcs or as flash-over arcs across insulators, or in the form of surface tracking or creepage along insulating surfaces, or in the form of corona or other types of electrical discharge.

Our prior Patent No. 2,768,264 discloses the use of hydrated alumina in electrical moldings to provide electrical insulating elements which have good physical strength and good electrical insulating properties, and which, when exposed to electrical arcing conditions, provide highly advantageous arc-suppressing and arc-quenching characteristics, and reduce the tendency of organic substances to carbonize on the surface of the material and form a conductive path.

The use of hydrated alumina in electrical moldings has become widespread and has permitted a great improvement in electrical apparatus in or about which arcing and other lelectrical `discharges must be controlled. Such use is common, for example, in switching apparatus, especially that for handling large currents at high voltages, and in various circuit interrupting devices both Aor" the single acting fuse type and reconnection types, where certainty of operation may wholly depend on the effective interruption and extinction of the arc formed between separated conductive elements. Hydrated alumina is also used in electrical insulating elements subject to external arcing phenomena, as in insulating supports for conductors and in transformer casings.

The role and action of hydrated alumina to give its irnproved results has been investigated by several investigators. For example, Kessel and Norman in Patent No. 2,997,526 disclose test apparatus and a test procedure for determining the arc-suppressing and especially the tracking resistant properties of-hydr-atedalumina compositions, and advance the explanation that the tracking resistant properties of hydrated -alumina compositions are due to an -oxidation action, in which aluminum oxide in the hydrated alumina catalytically promotes the oxidation of carbonaceous material. Further, the Ellsworth et al., Patent No. 3,071,661 uses the material of our prior patent to support the metal plates of an arc-chute structure in a circuit interrupter and notes that its property of gas evolution increases the speed of arc interruption and reduces erosion on the arc-chute structure, all with the result of increasing the arc-interrupting capacity and rating of the apparatus.

The present invention is based on the discovery that substantial improvement in the arc-interrupting charac- 3,242,257 Patented Mar. 22, 1966 teristics of molding compounds containing hydrated alumina can be obtained by the addition to the molding compositions of relatively small amounts of what may be termed arc-interrupting addition compounds,

Accordingly, it is the principal object of the invention to improve the arc-interrupting characteristics of electrical insulating moldings, such as the molded elements of electrical apparatus, by including small amounts of arc-interrupting addition compounds in the compositions of the molded elements, and thereby to improve the electrical performance of the moldings and the electrical apparatus. It is a further object of the invention to obtain such improvement over and .above the good .properties already lpresent in compositions containing substantial percentages of hydrated alumina. It is also an object o-f the invention to obtain improved arc-interruption while also retaining good surface-tracking resistance.

In accordance with the invention, electrical insulating moldings are modified by the presence of arc-interrupt.- i'ng addition elements or compounds in the molding co-mpositions of which they are composed, and such modification is obtained by adding the addition compounds to the molding compositions in their formulation.

The molding compositions to which the kaddition compounds are added in accordance with the invention comprise, generally, known electrical insulating molding compositions, including both hot-molded and cold-molded compositions. They include particularly compositions containing from 25% to 80% or more by weight of hydrated alumina and from 10% to 50% of a binder. In accordance with known practice, such compositions may also include substantialpercentages, up to say 60%, of filler material, such as clay flour and the like, and these may comprise materials which have desirable electrical properties of themselves, such as the aluminum oxide and magnesium oxide and hydrate mentioned in our prior patent. As part of or instead of ller, the compositions may also include fibrous reinforcing materials, such as glass fiber, asbestos ber, and the like.

The binders which may be used comprise various known organic binders including thermosetting binders, such as melamine, epoxy, urea, polyester, phenolic, and other known thermosetting resins; and rubber-like compounds, such as butyl and other synthetic elastomer compounds; and including thermoplastic binders, such as poly ethylene, polypropylene, polyamide, acetal, acrylic and other known thermoplastic resins. The binders which may be used also include inorganic binders, such as portland cement and mixtures of shale, clays, and lime as disclosed in United States Patent No. 1,852,672 to Petter et al.

The formulation and molding of the molding compositions may follow conventional practices known to the art. For example, in hot-molding compositions, the proportion of binder should be suicient to give the tluidity needed for the molding operation.

The Varc-interrupting addition compounds which may be used are compounds which will provide in the arcexposure surface of the molded insulating element a composition which will introduce arc-interrupting materials into the arc zone. By arc-exposure surface we mean a surface of an insulating element which -is exposed to arcing conditions. This may be an internal surface such as the inside surface of a switch enclosure or of an arc chute or the like, or the surface of an arc barrier between a pair of switches, or may be an external surface along which an arc may occur between conductive elements. Improved arc interruption will ordinarily be of greatest importance in arc enclosures Where the arcexposure surfaces are vsurfaces which define or enclose an arc chamber.

p ICC In arcing zones, the conditions present range from simple heating conditions at a distance from the arc path up to extreme and drastic conditions along and in the arc path' itself, land such conditions can produce and activa'te various chemical reactions, ranging from vaporization of low-boiling materials or of water of hydration up to changes involving partial or complete ionization, dissociation,l and decomposition of chemical compounds and their component parts.

While we do not fullyv understand the mechanism by which the improvements of the present invention are obtained, our experiments indicate that, in general, the addition compounds used should contain elements` (or radicals) having high electronegativity values, desirably values of the order of 2.0 or more, and that such components shouldbe present in compounds in which they are bound predominantly by covalent bonds rather than essentially by ionic bonds.

In accordance with the teachings of Linus Pauling (The Nature of the Chemical Bond), the bonds in monomolecular two-element compounds are considered predominantly covalent when the ele'ctronegativity difference between the bonded elements is less than about 1.7, and essentially ionic when the difference is greater, as in AlFa. However, the bonds may also be considered predominantly covalent, or effectively so, by other criteria, for example in the case of compounds containing more than two elements and two-elements compounds which form dimers or polymers, e.g. A12F6, and which then are predominantly covalent.

The addition compounds are preferably used in compositions which also contain substantial or large proportions of aluminum hydrate. With such hydrated alumina present in an arc-exposure surface in accordance with the prior art, the arc zone dened thereby will already have present therein, under arcing conditions, certain elements which have relatively high electronegativity values. These already-present elements include the non-metal elements nitrogen and oxygen from the air, which have electronegativity values of 3.0 and 3.5, respectively. 4They also include carbon, having lan electronegativity value of 2.5, as from carbon dioxide in theair orfrom organic binder material or'other carbonaceous'material which may' be'present'. They also include water'vapor derived from the water of hydration of the hydrated alumina, and may include ionization and dissociation products of the Water, including hydrogen which has an electronegativity value of 2.1.

It is not the purpose'of the present invention to add more of these electronegative elements which are already present under priorart conditions, for our experiments indicate that adding more of the same elements beyond a certain point, produces no -substantial improvement in arc interruption. Instead, the invention contemplates the addition of other and dierent highly-electronegative elements, and by this means to obtain improvements which are not obtained by adding more of an alreadypresent electronegative element.' However, the addition compounds may, Without harm, include components which add more of such already-present elements, for example, as water of hydration.

The highly-electronegative addition element maybe present in the composition of the arc-exposure surface as part of a chemical compound, and various compounds may be used. The compound must of course be of such character as to withstand the molding conditions used Y and to be compatible with the molding system. The

on suitable absorbent carriers or fillers, and these mayA be materials which are already present or may be matelected in the light of known incompatibilities.

rials added especially for this purpose. For example, carbon tetrachloride has been used by absorbing it on wood our which `is included in the molding composition, and it is found that sucient amounts of the absorbed liquid are carried through the molding procedure, even through molding temperatures above the normal boilingV point of the liquid, to provide an effective residue -in the composition of the arc-exposure surfaces of the moldedv part.

The addition compound must also be chemically compatible with the resin and other components of the molding composition, and addition compounds should be se- For example, ammoniumfcompound's should not be vused in water containing cold-mold compositions with a mel# amine binder, since in the presence of Water the ammonium and melamine react.

The addition compounds, in the amount-s used, must .also not destroy the insulating properties of the molded part.

Since the purpose is to introduce arc-interrupting material into the arc zone, the compounds used must be affected to this end by arcing conditions, and hence must be vaporized or partially or wholly dissociated in the presence of arcing.

When the addition compounds contain other elements beside the desired highly-electronegative elements, these others must not be deleterious in the compound or in the arc zone. This excludes compounds containing elements such as the alkali metals sodium and potassium, with which the highly electronegative elements form compounds having essentially ionic bonds. Such alkali metal compounds reduce rather than increase the arc-interruption properties of molding compositions.

In the light of the foregoing, arc-suppressing addition compounds which may be used in accordance with the present invention are compounds of the class consisting of (I) Inorganic compounds composed of (a) A member of the class consisting of atoms land ions of the following highly-electronegative elements:

Element: Electronegativity value Flourine 4.0 Chlorine 3.0 Bromine 2.8 Iodine 2.5 Sulfur 2.5 Phosphorous 2.1 Boron 2.0

and radicals composed of combinations of such named elements with others thereof, for example, -BF4, etc., and with others of the non-metal elements, for example, 804, -IPO4, -SiB, -B4O7, etc., combined With (b) A member of the class consisting of the ammonium radical, -NH4, and atoms Iand ions ofthe said abovenamed elements and of the following elements:

Element: Electronegativity value Magnesium 1.2 Aluminum 1.4 Zirconium 1.6 Zinc 1.0 Molybdenum 2.2

and

(II) Organic compounds of the class consisting of halogenated hydrocarbons, including halogenated lower aliphatic hydrocarbons such as carbon tetrachloride, perchloroethylene, tetrabromoethylene, etc., and halogenated paraffin waxes;

' which compounds are substantially stable solids or liquids conductive to maintain substantial insulating properties in the molded composition.

The desirable amounts of addition compound to be used may vary with the different addition compounds used, with the proportions of other components of thev composition, with the service in which the molded elements are to be used, and with other like factors. We find it generally true that relatively small amounts of the order of one percent (1%) or more give effective improvement, that small amounts may increase the additional improvement, but that little or no further improvement is obtained by greater amounts of addition compound. Generally, no further improvement in arc interruption is obtained by using more than about ten percent of the addition compound, but greater amounts will have no harmful effect on arc interruption and may be included for other desirable purposes or as a filler.

The addition compounds are desirably used in compositions which also contain large amounts of aluminum hydrate, in order to obtain the known arc-interrupting and track-resistant benefits of such compositions. We believe an interrelationship exists between the action of the aluminum hydrate and that of the addition compound, in which each aids the other to produce the over-al1 results obtained. Preferably, the addition compound is present in a minor proportion, of the order of 25 percent or less of the amount of aluminum hydrate present.

The accompanying drawings illustrate electrical apparatus which include electrical moldings in which the present invention may be embodied and the advantages thereof obtained. In such drawings:

FIG. 1 is an isometricrview of -a representative switch having a set of switch contacts enclosed by a hot-molded housing which provides physical support for certain of the contacts and whose inner surfaces constitute arc-exposure surfaces deiining an enclosure for arcs which may form between the contacts, and whose outer surfaces constitute arc-exposure surfaces which may be exposed to tiash-over arcs and may be subject to creepage tracking;

FIG. 2 is an isometric view of a circuit interrupter in which a wall of insulating material is drawn between enclosed -blade contacts when the circuit is opened and in which such wall and the enclosure walls may contain an addition compound in accordance with the invention;

FIG. 3 is an isometric View of Ia circuit interrupter of the type in which the arc which forms upon separation of the metal contacts is drawn between close fitting surfaces of electrical insulating moldings;

FIG. 4 is a sectional view of a fuse device in which the arc formed upon blowing of the fuse is contained within a molded insulating housing; and

FIG. 5 is a diagrammatic view of an experimental test apparatus.

The switch shown in FIG. 1 is a representative three phase switch having three closed switch compartments. Its housing comprises a base 10 -arranged for mounting on a suitable mounting plate 14 and having side walls 16 which support a bottom wall 18 spaced above the mounting plate 14. Above the wall 18, the side walls are interconnected by two spaced partitions 20y which, with the side and end walls, define the lower partsv of the three switch compartments. Each compartment has a central bottom opening bounded by anges 24 to slidably pass a carrier post 22. The housing cover 12 is of inverted box-like conliguration wit-h side walls 26 which carry a border ilange 27 interiitting with the side walls 16 of the base 10. The cover 12 contains two partitions 30 which interlit with the partitions 20' of the base and which with the side walls 26 and top wall 28 of the cover define the upper portions of the three switch compartments. In each compartment, the top wall 28 supports a pair of spaced contacts 3-2 carried by studs 34 whose upper ends are bolted to a pair lof terminals 36. The top surface of the cover 12 carries a longitudinal rib 38 separating the terminals 36 of each pair, and transverse ribs 40 separating the three pairs of terminals from each other. The ribs provide insulating arc barriers, and form extended surfaces between the conductors to increase the surface leakage pat-h.

In each switch compartment, the carrier 4.post 22 carries a shorting bar 42 having switch contacts 44 at its ends for engagement with the fixed contacts 32 when the carrier post 22 is raised. The carrier posts 22 of the three switches are interconnected by a cross bar 46 provided with an actuating arm 48 which extends downward through an opening in the mounting plate 14. Upward movement of the carrier posts 22 by the actuating arm 48 moves the shorting contacts 44 into engagement with the fixed contacts 32 to close the three phases of the switch, while downward movement opens the switch.

The switch of FIG. 1 is representative of switch devicesin which separable contacts are enclosed in compartments to conne the arcs which may occur when the switch contacts are opened and closed. The surface of the compartment walls constitutes arc-exposure surfaces in which addition elements may be `embodied in accordance with the present invention.

Another representative switch mechanism is shown in FIG. 2.r This -comprises a molded base 50 which carries two phase-barrier walls 52 and contains both a central longitudinal partition 54 and transverse partitions (not shown) aligned with the walls 52. In each phase section, the base supports a pair of L-shaped switch contacts 56, the long legs of which project through openings on opposite sides of the central partition 54 and stand as parallel switch -blades 57 resiliently biased toward each other. The short legs of each pair of contacts 56 are connected respectively to a line connector v58 and a fuse clip 59.

Connection between the switch blades 57 is controlled by a movable cross bar assembly 60 `comprising an actuating bar 62 connected to three separate legs 65 for the three phase sections of the switch. Each such leg comprises a snuffer housing 66 which encloses a pair o-f switch blades 57 and carries a central partition which, at the close-d end of the housing, consists of a shorting plate 68 for closing the circuit between the blades 57, and, at the open end of the housing, consists of an insulating wall 70. Retraction of the assembly 60 draws the shorting plate 68 out from between the plates 57 and pulls the insulating wall 70 between them, to intercept the circuit between them. The surfacesl of the snuifer housing 66 and of the partition 70 constitute arc-exposure surfaces which may desirably contain addition compounds in accordance with the present invention.

The circuit interrupter illustrated in FIG. 3 is for interrupting heavy power circuits. It comprises an outer cylindrical shell of a molded composition selected for its physical strength, lined with `a molded tubular liner 82 of a composition selected for its arc-interrup-ting characteristics. At spaced points along its length, the tubular assembly carries a pair of contact units each consisting of a fixed hollow stud 84 in which a contact 86 is spring pressed inward. For closing a circuit between the contacts, the shell assembly Sil-82 contains a slidable rod 88 which has a relatively close tting relation in the liner 82. The rod comprises a shorting spool 96 having lands 92 spaced to engage with the spring-pressed contacts 86 and having its center portion surrounded by an insulating sleeve 94 and its ends fixed in end pieces 96. The sleeve and end pieces, like the liner 82 are o-f a composition having arc interrupting characteristics which may 'be improved by the 'present invention.

When the rod assembly 88 is moved to bring the lands 92 into registry with the contact members 86, a largecapacity electrical circuit is closed between the two contacts 86. To open that circuit, the rod assembly is drawn .axially to carry the lands 92 out of registry with the contacts 86. When this is done, the arcs which form between the separating lands and contacts are drawn between the close fitting surfaces of the liner 82 and the insulating parts 94 and 96 of the rod, so that the physical confinement of the arcs, and the arc-interrupting characteristics of the material in .those surfaces cooperate to interrupt the arc.

FIG. 4 illustrates a conventional heavy duty fuse device, in which a fuse link or wire 100 is connected 'between a pair of connectors, here sho-wn as a cap 102 and `a sleeve 104, ycarried at the ends of a molded insulating tube 106 surrounding the fuse wire 100. 'I'he lower end of the molded insulating tube is left open to allow for expansion of gases which occur when the f-use blows. The inner surface o-f the molding insulating tube 106 constitutes an arc-exposure surface which may include an addition element in accordance with the present invention.

' The following examples illustrate the invention:

EXAMPLE l Polyester binder ammoniumr fluolborate additive The switching device used in this example was of a size suitable for 600-volt circuits, and included a replaceable molded insulating element having a surface extending along and close to the arc path between the electrical contacts of the device.

Molded insulating elements for this device were hotmolded, using a standard molding composition alone, and the same composition with the addition of two percent (2%) by weight of ammonium uoborate. 'Ihe components and proportions (by weight) of the standard composition were as follows:

Percent Polyester resin binder 25 Glass ber reinforcement Hydrated alumina 60 The binder components and the alumina were accurately weighed and were thoroughly mixed in a mechanical mixer. The glass fiber was then added and the mixing continued until the glass was thoroughly wetted. Weighed charges of the mixture were then placed in a heated die, the die was closed and held under pressure and heat until the composition was completely cured. The molded part was then removed from the die and given such finishing treatments as required, as to remove liashings, grind to tolerance dimensions, etc.

Switch tests were then carried out in the switching device, at 600 volts, using the different molded elements. In each test the current interrupted by the switching device was lirst set at a low figure, of the order of 100 amperes, and the switching device was operated several times to interrupt the circuit. The current was then increased, and the operation repeated at several current values. The procedure was continued until the current reached a value at which the switching device failed to interrupt the current upon the opening of its electrical contacts. With the molded element composed of the basic composition, and not containing ammonium fluoborate, the switching device failed to interrupt the circuit at a current value of 530 amperes. When, however, the molded element of standard composition was replaced with a molded element of the same composition but with the :addition of 2% ammonium fluoroborate along with the hydrated alumina, and the test repeated, the switching device interrupted the circuit at current values up to a maximum of 700 amperes. There was thus an increase in interrupting capacity for this device of 32%, obtained by including in the composition of the molded insulating element only 2% of ammonium iluoborate as an addition element. This substantially increased the capacity of the switching device, to permit it to be used at higher ratings, or to permit a switching device of the same rating to be made in a smaller physical size.

. 8 EXAMPLE 2 Polyester binder ammonium fluobomte additive The test apparatus used in this example was of the type shown in FIG. 3, adapted for switching high voltage power circuits, as of the order of l5 kilovolts. In such a device the arc between the metallic electrodes is drawn for a considerable distance between the inside surface of the cylindrical tube -82 and the outside of a closelyfitting rod 88 inside the tube, the difference in the diameters of the tube and rod being only a few thousandths of an inch. In this type of circuit interruptor, the arc interrupting properties of the insulating materials of which the rod and tube are composed can be measured by the amount of material on the tube and rod which is eroded away in a given number of switchings or circuit interrupt- -ing operations, that is, in a given number of arc extinguishing operations. To test our present invention as applied to high voltage circuit interrupter-s, circuit interrupters of the character described above were prepared, using different molding Icompositions to mold the tube and rod between which the arc is drawn. The basic composition used was the same as in Example l, which is a composition used commercially for arc-iuterrupters of this character. Identical arc-interrupters were prepared in which the tube and rod were made of the basic composition, and of the basic compositions with the addition of 5% ammonium fluoborate as an addition compound. The arc-interrupters were then operated under the same conditions to perform the same number of circuit interruptions, that is, to extinguish the same number of arcs. The circuit interrupters were then examined to determine the amount of material which had been eroded away on the rod and tube by the test operations.

In the unit in which the rod and tube were of the standard composition, not includ-ing an addition compound, 18 mgs. of material were eroded away. In the arc interrupter in which the rod and tube contained 5% ammonium fluoborate as an addition compound, only 4.6 mgs. were eroded away by the test operations. The results of these tests show that the addition of 5% of ammonium fluoborate to the molding composition produced a substantial improvement in the quality and operations of the arc interrupter, and caused the arcs to be extinguished more eihciently, sooner, and at a shorter length.

EXAMPLE 3 Polyester resin binder ammonium fluoborate additive Test apparatus was prepared as shown in FIG. 5. A xed support was arranged to receive a test specimen 112 with the top surface of the specimen engaged by a fixed contact 114 and a movable contact 116 moved by reciprocating rod 118 driven from an adjustable eccentric or crank 120. The two contacts 114 and 116were connected in a 110-volt electrical circuit between a pair of supply wires 122 and 124, with the contacts in series with an adjustable load 126 and with a sensitive watt-hour meter 128 connected to measure the electrical energy in the circuit. In operation, the reciprocating device was arranged to move the contacts 114 and 116 close enough to strike an arc between them, and then to separate the movable contact 116 from the fixed contact 114 to draw the arc across the surface of the test specimen 112 a suicient distance to cause the arc to be extinguished. In the test of each specimen, the energy expended by the arc was recorded over a series of l0 cycles, and the results averaged. Different test specimens were tested under the same conditions; The difference in energy measured in the different tests was taken to indicate the comparative arc-interrupting properties of the material of the test specimens. Materials with better arc-interrupting properties caused the arc to be extinguished sooner and at a shorter length, so that the energy measured for the arc of shorter length and duration indicated the improved arc-interrupting properties of the material.

A series of test specimens were molded using the composition of Example 1 alone, and that same composition with the addition of ammonium fluohorate in different amounts ranging from 1% to 10% by Weight; and the test specimens so prepared were tested on the apparatus shown in FIG. 5. All tests of specimens containing am-y monium uoborate showed improvement in the interrupt- EXAMPLE 4 Polyester resin binder-various additives A molding compound of a conventional composition consisting of 28% polyester resin binder and 72% hydrated alumina was prepared, and test specimens were molded from this basic composition alone and from the same composition with the addition of varying percentages of addition compounds as indicated below. The test specimens were tested in the apparatus shown in FIG, 5, by the procedure described in Example 3. The electrical power supply and the adjustments of the variable load 26 and of the reciprocating drive 20 were the same throughout the comparative tests. The basic composition was used as a standard of comparison for the results obtained with the compositions containing addition compounds, and the results obtained were as follows:

Composition Watt-hours Comparative percentage 28% polyester resin and 72% hydrated alumina 0719 100 Same, plus 10% ammonium fluoborate- 04210 58. 5 Same, plus magnesium tluosilicate.. 0259 36. Same, plus ammonium fluosilicate.. 0292 40. 5 Same, plus zinc iluoborate 044 61. 3 Same, plus 10% chlorinated paraliln wax. 044 61. O Same, plus 10% zirconium oxychloride- 0435 60. 5 Same, plus 10% zirconium tetrachloride- 044 61.0 Same, plus 10% ammonium luoborate- 0309 53 Same, plus 10% ammonium chloride 0383 65. 7 Same, plus 10% ammonium bromide .0360 61.8 Same, plus 10% ammonium biiluoride-.- 0456 78. 2 Same, plus 10% ammonium suli'lte 0456 61.5 Same, plus 10% sodium iluoride.- 1060 182.0 Same, plus 10% potassium nitrate 10800 150. 0

It is noted that with the sodiumand potassium-containing compounds, the composition had a reduced arcinterrupting capacity. The presence of these highly ionic elements thus had a deleterious eiect and should be avoided.

EXAMPLE 5 Polyester resin bindervarious ammonium compound additives Composition Watt-hours Comparative percentage 25% polyester resin, 15% glass ber, 60%

hydrated alumina 0740 100 Same, plus 5% ammonium bromide.- 0565 76. 4 Same, plus 5% ammonium sulfate 0646 87. 4 Same, plus 5% ammonium bifluoride 0540 73. 0 Same, plus 5% ammonium pentaborate- 0540 73.0 Same, plus 5% ammonium biborate 0467 63. 1 Same, plus 5% ammonium chloride. 0504 68. 0 Same, plus 5% ammonium Iiuoborate- 0518 70. 0

10 EXAMPLE 6 Example 3 was repeated using test specimens molded from the4 same basic composition and from that composition with varying amounts of ammonium iiuorborate. The results obtained were as follows:

Melamine resin binder This example was carried out with the test apparatus shown in IFIG, 5, in the same manner described in Example 3. The Ibasic composition was a cold-molded composition comprising 25% melamine resin and 75% hydrated alu-mina. In cold-molded compositions employing organic binders, the ingredients are preferably iirst blended in a dry state. The blended dry mixture is then wetted with an agent capable of liquefying or softening the binder, and mixing is continued. The wet mixture is then granulated and molded under pressure into the desired shape. Following the molding'operation the devices are cured in baking ovens under elevated temperature which gradually increases to a maximum of 300 400 F.

Test specimens were prepared in this Way from basic composition alone and With the addition of 10% of certain addition compounds, as indicated below. The results obtained were as follows:

Composition Watt-hours Comparative percentage 25% melamine resin, 75% hydrated alumina.. 0813 Same, plu

(AhF 0471 58.0 Same, plus 10% chlorinated paraffin t x. 0529 65` 2 Same, plus 10% aluminum phosphate- 0656 81. 0

These results show that the use of addition compounds in accordance with the invention is effective in cold molded compositions in which the binder is a melamine resin.

EXAMPLE 8 Phenolic resin Composition Watt-hours Comparative percentage 28% phenolic resin, 72% hydrated alumina 0935 100 Same, plus 10% aluminum iiuoride 2 s 0542 58. 0 Same, plus 10% chlorinated paraliin wax 0636 63. 6 Same, plus 10% aluminum phosphate 0715 76. 5

These results show that the use of addition compounds in accordance with the invention is effective in molding compounds in which the binder is a phenolic resin.

1 1 EXAMPLE 9` Inorganic binder Addition compounds in accordance with the invention may also be used in cold-molding compositions containing inorganic binders. With such compositions, the ingredients are rst blended dry, Water `is added, and mixing continued. After a granulating step, the composition is molded into the desired form, and the molded shapes are cured either by aging or by subjecting them to saturated steam under pressure. After drying at 400 F. or there abouts, the molded shapes may .be immersed in molten Wax to impregnate them and reduce the tendency -of the material to absorb moisture. An example of such a composition is as follows:

Percent Portland cement 35 Asbestos fiber 121/2 Hydrated alumina 471/2 Aluminum uoride (AlZFe) 5 When a cold-molded composition of this type is immersed in Wax to reduce Water absorption, the arc-interrupting addition compound may be incorporated in the composition of the surface portion of the part by including it in the Wax, for example, by using a halogenated Wax.

EXAMPLE l0 Example 1 is repeated, save that instead of using polyester resin as the binder, phenolic resin in one case, and melamine resin in another case was used as the binder in hot molded composition. The resulting moldings gave improved .arc-interruption, as in other examples.

We claim as our invention:

1. A molded electrical insulating element having an arc-exposure surface adapted to extend along an electrical arc Zone, the composition of the material of said molded element at said surface consisting essentially of a binder, a substantial proportion of hydrated alumina, and a small proportion, suicient to increase lthe arc-interrupting characteristics of the composition, of an arc-interrupting :addition compound consisting essentially of a strongly electronegative element of the class consisting of iluorine, chlorine, .bromine, iodine, sulfur, phosphorous and boron, bound in the compound by predominantly covalent bonds, thel'compound being substantially sta-ble at normal temperature, substantially non-reactive With other components of the composition, :and non-conductive in the proportions present.

2. A molded electrical insulating element as set forth in claim 1 in which said arc-exposure surface material consists essentially of from to 50% of binder and from 25 to 80% of hydrated alumina, byweight, and the addition compound.

3. A molded electrical insulating element as set forth in claim 2 in which the addition compound is present in the proportion from approximately 1% to 10% by Weight.

i4. A molded electrical insulating element as set forth in claim 1 in which the addition compound is present in the proportion by Weight of at least about 1% of the total composition and not more than 25% of the aluminum hydrate present.

5. A molded electrical insulating element having an arc-exposure surface adapted to extend along an electrical arc zone, the composition of the material of said molded element at said surface consisting essentially of a binder, a substantial proportion of hydrated alumina, and a small proportion sufficient to increase the arc-interrupting characteristics of the composition, of an arc-interrupting addition compound of the Aclass consisting of inorganic compounds composed of (a) a member of the class consisting of atoms and ions of the highly-electronegative elements uorine, chlorine, bromine, iodine, sulfur, phosphorous, and boron, and radicals composed of combinations of such named elements with others thereof and with others of the non-metal elements, combined with (b) a member of the class consisting of the ammonium radical, -NH4, and atoms and ions of the said above-named elements and of the elements magnesium, aluminum, zirconium, zinc, Iand molybdenum, and

organic compounds of the class consisting of halogenated hydrocarbons and halogenated paraflin waxes; which compound is a substantially stable solid or liquid at molding temperatures, is substantially non-reactive in the molding composition under molding conditions, and is substantially non-conducting in the proportions present;

6. A molded electrical insulating element as set forth in claim 5, in which the addition compound is an inorganic salt.

7. A molded electrical insulating element as set forth in claim 5, in which the addition compound is a halogenated lower aliphatic hydrocarbon.

8. A molded electrical insulating element as set forth in claim 5, in which the addition compound is a halogenated paraiiin Wax.

9. A molded electrical insulating element as set forth in claim 5, in which the addition compound is present in a proportion by Weight of at least about 1% of the total and not more than 25% of the aluminum hydrate present.

10. In electrical apparatus subject to arcing, a molded insulating element having an arc-exposure surface confronting a zone in which arcing may occur, the composition of the material of said element at said surface consisting essentially of a binder, a substantial proportion of hydrated alumina, and a small proportion sufficient to increase the arc-interrupting characteristics of the composition, of an arc-interrupting addition compound consisting essentially of a strongly electronegative element of the class consisting of uorine, chlorine, bromine, iodine, sulfur, phosphorous and boron, bound in the compound by predominantly covalent bonds, the compound being substantially stable at normal temperature, substantially non-reactive with other components of the composition, and non-conductive in the proportions present.

11. In electrical apparatus subject to arcing, a molded insulating element having an arc-exposure surface confronting a zone in which arcing may occur, the composition of the material of said element at said surface consisting essentially of a binder, a substantial proportion of hydrated alumina, and a small proportion suflicient to increase the arc-interrupting characteristics ofthe composition, of an arc-interrupting addition compound of the class consisting of inorganic compounds composed of (a) a member of the class consisting of atoms and ions of the highly-electronegative elements fluorine, chlorine, bromine, iodine, sulfur, phosphorous, and boron, and radicals composed of combinations of such named elements with others thereof and with others of the non-metal elements, combined With (b) a member of the class consisting of the ammonium radical, -NH4, and atoms and ions of the said abovenamed elements and of the elements magnesium, aluminum, zirconium, zinc, and molybdenum, and

organic compounds of the class consisting of halogenated hydrocarbons and halogenated parailin waxes; which compound is a substantially stable solid or liquid at molding temperatures, is substantially non-reactive in the molding composition under molding conditions, and is substantially non-conducting in the proportions present.

12. A molding composition for electrical insulating moldings having'improved arc-interrupting characteristics, consisting essentially of from 25 percent to 80 percent by weight of hydrated alumina,

at least percent of binder, and

an effective amount of from about 1 percent to l0 percent of an arc-interrupting additive compound,

said compound consisting essentially of a stronglyelectronegative element of the class consisting of iluorine, chlorine, bromine, iodine, sulfur, phosphorous, and boron, bound in the compound by predominantly covalent bonds.

the compound being substantially stable and non-reactive in the composition at the molding temperature thereof, and being non-conductive in the composition When in molded state.

13. A molding composition for electrical insulating moldings having improved arc-interrupting characteristics, consisting essentially of from 25 percent to 80 percent by Weight of hydrated alumina,

at least 10 percent of binder, and

an effective amount of from about 1 percent to 10 percent of an arc-interrupting additive compound of the class consisting of inorganic compounds composed of (a) a member of the class consisting of atoms and ions of the highly-electronegative elements uorine, chlorine, bromine, iodine, sulfur, phosphorous, and boron, .and radicals composed of combinations of such named elements with others thereof and with others of the non-metal elements, combined with (b) a member of the class consisting of the am monium radical, -NH4, and atoms and ions of the said abovenamed elements and of the elements magnesium, aluminum, zirconium, zinc, and molybdenum, and

organic compounds of the class consisting of halogenated hydrocarbons and halogenated parain waxes; which compound is a substantially stable solid or liquid at molding temperatures, is substantially non-reactive in the molding composition under molding conditions, and is substantially non-conducting in the proportions present.

14. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is an ammonium salt.

15. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a liuoborate.

16. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a magnesium salt.

17. A molding composition as set forth in claim 13 in 50 which the arc-interrupting additive compound is an aluminum salt.

18. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a chlorinated hydrocarbon.

19. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is ammonium iluoborate.

20. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a fluorine-containing salt.

21. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a halogen-containing compound.

22. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a halogen-containing ammonium salt.

23. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is a borate.

24. A molding composition as set forth in claim 13 in which the arc-interrupting additive compound is an ammonium borate.

25. In a molded electrical insulating element comprising a molded composition consisting essentially of a binder and a substantial proportion of hydrated alumina, the improvement which consists of an arc-interrupting addition compound interspersed through the composition with the hydrated alumina and comprising a strongly electronegative element of the class consisting of lluorine, chlorine, bromine, iodine, sulfur, phosphorous and boron, bound in the compound by predominantly covalent bonds, the compound being substantially stable at normal temperature, substantially non-reactive with other components of the composition, and non-conductive in the proportions present.

26. A molded electrical insulating element as set forth in claim 25 in which the molded composition also contains a filler.

27. A molded electrical insulating element as set forth in claim 25 in which the molded composition also contains a glass fiber reinforcement.

References Cited by the Examiner UNITED STATES PATENTS 1,786,581 12/1930 Steerup 252-63.5 2,768,264 10/ 1956 Jones et al. 252-63.2 X 2,830,919 4/ 1958 Schatzel. 2,961,518 11/1960 Hermann. 2,997,528 8/ 1961 Kessel et al. 260-40 X FOREIGN PATENTS 586,802 4/ 1947 Great Britain.

JOHN F. BURNS, Primary Examiner.

LARAMIE E. ASKIN, Examiner. 

25. IN A MOLDED ELECTRICAL INSULATING ELEMENT COMPRISING A MOLDED COMPOSITION CONSISTING ESSENTIALLY OF A BINDER AND A SUBSTANTIAL PROPORTION OF HYDRATED ALUMINA, THE IMPROVEMENT WHICH CONSISTS OF AN ARC-INTERRUPTING ADDITION COMPOUND INTERSPERSED THROUGH THE COMPOSITION WITH THE HYDRATED ALUMINA AND COMPRISING A STRONGLY ELECTRONEGATIVE ELEMENT OF THE CLASS CONSISTING OF FLUORINE, CHLORINE, BROMINE, IODINE, SULFUR, PHOSPHOROUS AND BORON, BOUND IN THE COMPOUNDS BY PREDOMINANTLY COVALENT BONDS, THE COMPOUND BEING SUBSTANTIALLY STABLE AT NORMAL TEMPERATURE, SUBSTANTIALLY NON-REACTIVE WITH OTHER COMPONENTS OF THE COMPOSITION, AND NON-CONDUCTIVE IN THE PROPORTIONS PRESENT. 